Cleaning and degassing operations in underground fuel storage tanks are traditionally carried out by first emptying the tank, using a suction pump, and then lowering an operative into the tank itself, who, using special tools guaranteed not to produce any sparks which might cause an explosion, then scours the internal part of the tank; said operative also being provided with a suction mouth, guided by him, for removing by aspiration the sludge gathered at the bottom of the tank.
This operation is in reality extremely dangerous, due to the presence of inflammable vapours inside the tank, liable to cause explosions and possibly the death of the operator.
Further, the cleaning operation carried out by the operator requires great use of cleaning water, which also has to be collected up and suitably dispersed.
Instead of employing an operator to be introduced inside of a fuel storage tank, JP-A-4,038,496 discloses a travelling truck which can be inserted into a container to be cleaned.
Said truck is able to clean the side walls, the ceiling and the floor of the container by means of water injected from suitable nozzles, at the end of the cleaning operation said water being received by side covers positioned on both sides of the truck and then collected in the corner to be sucked by a suction pipe.
Furthermore, U.S. Pat. No. 4,770,711 discloses a portable hydraulic apparatus for cleaning the hydrocarbon contaminated sludge deposit of an oil storage tank by means of a fluidizing agent.
Said apparatus comprises a frame, having a central portion and first and second end portions, and a couple of independently movable endless chain belts suitable to move the frame within the oil storage tank; the fluidizing agent is discharged into selected portions of the sludge deposit so as to form a pool of sludge and fluidizing agent.
Then, a suction pump positioned on the central portion of the frame draws up said pool. Moreover, a plurality of nozzles is disposed adjacent the first end portion of the frame and is connected with the suction pump so as to provide pressurized agitation and discharging of the pool into a second portion of the sludge deposit adjacent said first end portion of the frame so as to dislodge and also aid in liquifying the second portion of the sludge deposit.
Document JP-A-3,137,955 describes a small robot to be used in hazardous environments wherein it is immersed in liquid and motioned by means of main endless tracks on both side of a main shaft and of auxiliary endless tracks at the front and rear ends of the main shaft via a rotative auxiliary chassis.
Moreover, document U.S. Pat. No. 4,817,653 discloses a water washing robot which comprises a frame provided with water pumps means, robot articulations means disconnectably mounted on the frame and nozzled articulatable wash water jetting means disconnectably mountable on the frame.
The robot is transported, in unassembled form, inside of oil storage tanks and assembled therein to be used in cleaning operations. One operator is required inside the storage tank to control the robot moving and working phases.